Polyvinyl acetals are commercially valuable resins used as interlayers for safety glass, in adhesives, as epoxy resin plasticizers and as wash primers. They are derived from the reaction of poly(vinyl alcohol) with aldehydes, but can be prepared by a one-step process in which a poly(vinyl ester), such as poly(vinyl acetate), is simultaneously saponified and acetalized.
The properties of polyvinyl acetals depend upon the method of preparation and the proportion of residual unhydrolyzed ester groups, the number of alcohol groups and the percentage of acetal moieties contained in the polymer. For example, in the preparation of safety glass, a polyvinyl butyral is used having a small amount of vinyl acetate, about 9% of vinyl alcohol groups, and about 70-80% of vinyl butyral groups. Polyvinyl butyral resins used in wash primers have about 2-3% of residual vinyl acetate in the polymer. Other applications, such as in specialty adhesives, textile coatings or strippable coatings require different polymer compositions.
One method of modifying the properties of polyvinyl acetals has been to change the functionality of monomers making up the polymer, such as employing a comonomer with the vinyl alcohol monomer, such as acrylonitrile, vinyl chloride, acrylate and the like. A discussion of polyvinylacetals and such modification using acetalized vinyl alcohol copolymers is given by Lindemann, Encyclopedia of Polymer Science and Technology, Volume 14, pages 208-239 (1971). It is desirable however to improve on the forms and functionality of polyvinylacetals in order to increase their potential utility.
Amine functional polymers are valuable as a cost effective way of incorporating cationic charge into polymers useful in cationic electrocoating, water treatment, and enhanced oil recovery (EOR). U.S. Pat. No. 4,843,118, Lai et al. (1989) discloses the use of high molecular weight (&gt;1.times.10.sup.6) poly(vinylamines) in acidized fracturing fluids for EOR. Such poly(vinylamines) can be prepared by acid or base hydrolysis of poly(N-vinylformamide). Although the high molecular weight poly(vinylamines) can be used in EOR without crosslinking, the use of crosslinking agents, such as epichlorohydrin, hexamethylene diisocyanate and glyoxal, is disclosed as optional. The use of a dialdehyde, such as glyoxal, to crosslink poly(vinylamine) is also disclosed in Japanese Patent Publication No. J61051006 (1986).
In the treatment of municipal wastewater and similar wastewaters obtained from other sources than municipalities, it is an objective to achieve final disposal of the waste in a manner that is both cost effective and environmentally safe. To do this, the treatment facility must effectively separate the suspended solids material from the water to produce a high solids sludge cake which can be economically handled and a clear effluent which meets governmental standards required for return of such water to surface water, such as streams, rivers and lakes.
Inorganic salts, such as FeCl.sub.3 have been used for many years to help separate the suspended solids particles from the wastewater. These salts reduced the negative charges on the particles and aided them in settling. One problem with inorganic salts is that high concentrations are needed for them to be effective, adding considerable weight to the resultant sludge cake. This additional weight substantially increases disposal costs. Also many of the inorganics leave behind unacceptable levels of heavy metals which can harm the environment. These metals and salts also interfere with attempts to incinerate the sludge cake.
At the present time, polymers, usually cationic polymers, have largely replaced the inorganic salts. These polymers are typically of a high molecular weight, on the order of 1 million or above. For example, U.S. Pat. No. 4,705,640 to Whittaker (1987) describes a number of organic polymeric flocculants having very high molecular weight which can be degraded in solution mechanically to lower molecular weight products which still have an intrinsic viscosity above 4 and a molecular weight above 1 million, typically up to 30 million.
Use of a cationic polymer negates the negative charge on suspended particles and then binds those particles together, improving separation and facilitating the dewatering step. Generally such polymers are needed at lower dosage levels than the inorganic salts, and this has the advantage of minimizing sludge weight and overall costs. Polymers are also compatible with sludge incineration. Polymers in use currently are typically cationic homopolymers or cationic copolymers with acrylamide.
U.S Pat. No. 4,217,214, Dubin (1980), discloses using a poly(vinylamine) hydrochloride having a molecular weight above 3.times.10.sup.5 as a flocculant in treating aqueous suspensions.
U.S. Pat. No. 4,421,602, Brunnmueller, et al. (1983), discloses a partially hydrolyzed homopolymer of N-vinylformamide useful as a drainage aid in papermaking. In this polymer from 10 to 90% of the formyl groups are hydrolyzed to amine units in either acid or base.
U.S. Pat. No. 4,808,683, Itagaki, et al. (1989), discloses a vinylamine copolymer of N-vinylformamide and an alkyl or oxyalkyl N-substituted acrylamide or methacrylamide in which the formamide units have been partially hydrolyzed under acidic conditions to cationic amine units. The copolymer is said to be useful as a flocculating agent for treating wastewater, for dehydrating organic sludge and in papermaking.
U.S. Pat. No. 4,952,656, Lai, et al. (1990), discloses poly(vinylamine)s of very high molecular weight, e.g.. 3.6.times.10.sup.6 to 9.times.10.sup.6, made by inverse emulsion polymerization, which are useful as flocculants.
U.S. Pat. No. 4,957,977, Itagaki, et al. (1990) discloses the use of vinylamine copolymers from N-vinylformamide and acrylonitrile or methacrylonitrile useful as a cationic flocculating agent for wastewater, as a dehydrating aid for organic sludges, and as a paper strength-increasing agent.
U.S. Pat. No. 5,037,927, Itagaki (1991), describes a copolymer of N-vinylformamide and an acrylate ester, such as methylmethacrylate, hydrolyzed to a poly(vinylamine) under acidic conditions, which is said to be useful not only in papermaking, but also as a cationic polymeric flocculating agent for treating wastewater and dehydrating organic sludges.
While there are many polymeric flocculating agents available, both commercially and in the literature, for use in treating wastewater, the needs of the wastewater industry are almost as diverse as the number of facilities engaged in wastewater treating and disposal. It is highly desirable, therefore, that other methods of treating wastewater, particularly from municipalities, using polymeric flocculating agents be developed in order to minimize treating costs and enable waste systems to operate without an adverse impact upon the environment.